Flexible couplings for connecting one component to another component are well known. One identified use for flexible couplings is for connecting a drive source, such as a motor, to a peripheral device, in which the components are susceptible to initial misalignment, or due to the nature of the components, are dynamically misaligned in use.
Another identified use for flexible couplings is for reducing the transmission of stress and vibrations between two or more connected components. For example, drilling assemblies used by the oil and gas industry, for retrieving various fluids and gases buried within earth formations, typical comprise a drilling string connected to a drill bit. The drilling string comprises a plurality of interconnected pipe segments with the drill bit positioned at a distal end thereof. As the drill bit cuts through the earth, vibrations, usually at high frequencies, occur and are transmitted along the drilling string. These high frequency vibrations may cause fatigue, deterioration, and finally failure of the components of the drilling assembly. In addition, drill string sections may comprise highly sensitive electronic devices, such as those associated with MWD (Measuring While Drilling) systems. The electronics must be isolated from the same high frequency vibrations, as well as, other applied stresses. Furthermore, the electronic devices must be isolated from torsional loads that occur during acceleration or deceleration of the section carrying the electronics.
William Turner and Russell Ide, in U.S. Pat. No. 5,833,541 (“the '541 patent”), describe an elastomeric coupling for suppressing shocks and vibrations associated with down hole drilling assemblies. As can be seen in FIGS. 1-2, the coupling includes an interlocked male member 1 and female member 2, each member having threaded portions, and an elastomer 3 filling the spaces between the threaded portions. Under loading the male and female members are capable of moving relative to one another. The inventors of the '541 patent disclose a method of preserving coupling integrity under a “loosening” torque, comprising a plurality of locking plugs The plugs 5 are inserted into the assemblies after the male portion is threaded into the female portion, but before the elastomer is provided The locking plugs extend through a wall of the female member 2 and between adjacent thread turns extending from an outer surface of the male member 1. This arrangement substantially prevents the male threaded portion from being unscrewed from the female threaded portion.
Although a useful contribution to the arts, the coupling integrity preserving method described in the '541 patent has some disadvantages. The locking plugs are prone to failure due to stress concentrating on the plugs. After the plugs fail, the male and female members can decouple upon the presence a sufficient reverse torque. Moreover, it is extremely difficult to properly position the plugs such that they are functional, yet do not act as a stress/vibration transmission conduit, which will occur if any portion of the plug contacts the male member.
Accordingly, a need exists in the art for a flexible coupling that once assembled, will not decouple in any direction due to torsional loads, can effectively attenuate vibrations and other applied stresses, and/or can effectively transmit torque.